1. Field of the Invention
The present invention relates in general to a sub Chip On Board (COB) for optical mouse, and more particularly to a sub chip on board formed by directly attaching an IC chip to a sub printed circuit board (hereinafter, referred to as PCB) and mounting the sub PCB on a main PCB with pins.
2. Description of the Prior Art
Generally, an optical mouse is operated by reflecting light emitted from the main body of the optical mouse from a touching object (for example, a mouse pad), thus, enabling the movement of the mouse on the pad to be detected and enabling a cursor on a computer monitor to be moved. The optical mouse is a pointing device (or a display cursor control device) clicked by the user, and an input device independent of a keyboard. Particularly, the optical mouse has several advantages such as its precise detection of a movement of user""s hand and its smooth movement, compared with a conventional ball mouse, thus its use increasing more and more. Such an optical mouse optically recognizes its movement on the touching object, converts the recognized value to an electric signal, transmits the electric signal to the computer, and thereby the position of the cursor on the monitor can be recognized.
FIG. 1 is a side view showing a conventional optical mouse. Referring to FIG. 1, the optical mouse 10 includes a light emitting unit 12, a lens 13, an IC chip 15 having an optical sensor 16, and a PCB 14 in a casing 11. Further, at the top of the mouse 10, a button 18 for being clicked by the user is arranged. The light emitting unit 12 has a conventional LED (Light Emitting Diode) for emitting light, and the lens 13 concentrates the light reflected from the mouse pad 20. The optical sensor 16 of the IC chip 15 senses the concentrated light. The PCB 14 is connected to the IC chip 15 through a lead frame 19.
In the optical mouse 10, if the light emitting unit 12 emits light, the light is radiated to the mouse pad 20. The radiated light is reflected from the mouse pad 20. At this time, the reflected light from the mouse pad 20 is concentrated by the lens 13. If the concentrated light from the lens 13 is projected to the optical sensor 16, the optical sensor 13 senses the projected light, thus recognizing the movement of the mouse 10 on the pad 20. As described above, the optical mouse 10 senses the light, and so the moving direction and distance of the mouse 10 is recognized. The recognition result is converted into an electric signal, and the electric signal is transmitted to a computer. Thereby, the user moves the optical mouse 10 on the mouse pad 20 to display the position of the cursor on the monitor.
Further, the optical mouse requires a construction enabling it to recognize received light and transmit it to the PCB. The construction for arranging the PCB and IC chip in an optical mouse is disclosed in U.S. Pat. Nos. 4,521,772 and 4,751,505. Referring to the optical mouse construction disclosed in U.S. Pat. No. 4,521,772, an IC chip having a sensor array is separated from a PCB, and is attached to a support element arranged vertically on the PCB. Further, referring to the optical mouse construction disclosed in U.S. Pat. No. 4,751,505, a packaged IC circuit device having a plurality of pins is mounted on a PCB.
FIGS. 2 and 3 are views showing the construction of a conventional chip on board mounted in a typical optical mouse. Referring to FIGS. 2 and 3, an IC chip 150 having an optical sensor 160 is manufactured in a package, and the packaged IC chip 150 is mounted on a PCB 100. The IC chip 150 having the optical sensor 160 is wire-bonded to a lead frame 170. Further, transparent resin 190 is spread on the bottom surface of the IC chip 150. Further, a cap 180 having a hole 181 for passing received light is covered on the transparent resin 190. As described above, a chip on board manufacturer purchases fully-packaged IC chips having the above construction, and mounts them on the PCBs 100. Referring to FIGS. 2 and 3, in the construction of the conventional chip on board, the IC chip 150 is mounted on the PCB 100 through the lead frame 170, and is supported by the lead frame 170, thus being arranged on the PCB 100. Further, a path 101 for guiding received light is arranged on the PCB 100.
On the other hand, in U.S. Pat. No. 4,751,505, a construction for mounting a packaged IC chip having pins without lead frames on a PCB is disclosed. However, the construction disclosed in U.S. Pat. No. 4,751,505 is problematic in that its manufacturer must purchase the packaged IC chips from the chip manufacturer and mount them on the PCBs, in the same manner as that described for the chip on board of FIGS. 2 and 3.
As described above, the conventional chip on board for optical mouse is disadvantageous in that a chip on board manufacturer must purchase fully-packaged sensor IC chips, including lead frames used for bonding the IC chips to PCBs, from a chip manufacturer, and mount the chips on the PCBs. Moreover, the conventional chip on board is problematic in that it requires a casing for protecting the packaged IC chip, thus increasing the manufacturing costs and decreasing the manufacturing efficiency.
Therefore, the present invention has been made in view of the above problem, and it is an object of the present invention to provide a sub chip on board for optical mouse, for directly attaching a sensor die having an optical sensor to the bottom surface of a sub PCB, directly wire-bonding the optical sensor to the sub PCB, and mounting the sub PCB on a main PCB with pins, thus reducing the manufacturing costs and improving the manufacturing efficiency.
It is another object of the present invention to provide a sub chip on board for optical mouse, having a sub PCB having a sensor die directly attached on the bottom surface of the sub PCB.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of sub chip-on board for optical mouse, comprising a sub PCB having both a plurality of input/output pads and a plurality of pin holes; a sensor die having an optical sensor wire-bonded to said input/output pads for sensing received light, and being attached to a bottom surface of the sub PCB; a transparent resin covering the sensor die at the bottom surface of the sub PCB; a cap attached to the bottom surface of the sub PCB such that the cap covers the transparent resin, and having a hole for guiding the received light to said optical sensor; a main PCB having both a hole for guiding the received light to the optical sensor and a plurality of pin holes corresponding to the pin holes of the sub PCB; and a plurality of pins commonly inserted into the pin holes of both the main PCB and the sub PCB such that the sub PCB is fixed on the main PCB.